This comes about 5 years too late for my wife and myself. In 2014, we both lost our United accounts. We had tried to save the miles by getting magazines but 3 weeks was not enough time for the process to occur. At that time, we had other worries such as selling our house for a move to the UK so let it go. After all, our main airline was US Airways...... And then it became BA....
Two years later, we did come back to the US to a location where United was the common sense choice. When my account was closed, I did not lose many miles as I had only occasionally flown with United. My wife did not lose many miles as she had used her miles for Business Class tickets on international long-hauls. But, now, that reluctantly she rejoined United (in her mind we were going to keep our BA Gold and Silver levels), she realized that she lost 300,000 United lifetime miles. She had that lost account since 1986.....